Means to improve center-to edge uniformity of electrochemical mechanical processing of workpiece surface

ABSTRACT

An electrochemical mechanical process for electroplating or electropolishing a conductive surface of a wafer is provided. The conductive surface of the wafer is touched by a polishing surface of a compressible pad while a process solution flows through the pad and a potential difference is maintained between the conductive surface and an electrode. The pressure between the polishing surface and a central region of the conductive surface is increased by applying a shaping process to either the conductive surface or the pad.

RELATED APPLICATIONS

[0001] This application claims priority from Provisional PatentApplication Ser. No. 60/462,919 filed on Apr. 4, 2003 (NT-295 P), andthis application is a continuation in part of U.S. patent applicationSer. No. 10/152,793 filed on May 23, 2002 (NT-102 D) which is adivisional of U.S. patent application Ser. No. 09/511,278 filed Feb. 23,2000 (NT-102) which is now U.S. Pat. No. 6,413,388, all incorporatedherein by reference.

FIELD

[0002] The present invention generally relates to semiconductorintegrated circuit technology and, more particularly, to a device forelectrotreating or electrochemically processing a workpiece.

BACKGROUND

[0003] Conventional semiconductor devices such as integrated circuits(IC) generally comprise a semiconductor substrate, usually a siliconsubstrate, and a plurality of conductive material layers separated byinsulating material layers. Conductive material layers, orinterconnects, form the wiring network of the integrated circuit. Eachconductor in the wiring network is isolated from the neighboringconductors by the insulating layers, also known as interlayerdielectrics. One dielectric material that is commonly used in siliconintegrated circuits is silicon dioxide, although there is now a trend toreplace at least some of the standard dense silicon dioxide material inIC structures with low-k dielectric materials such as organic,inorganic, spin-on and CVD candidates.

[0004] Conventionally, IC interconnects are formed by filling aconductor such as copper in features or cavities etched into thedielectric interlayers by a metallization process. Copper is becomingthe preferred conductor for interconnect applications because of its lowelectrical resistance and good electromigration property. The preferredmethod of copper metallization process is electroplating. In anintegrated circuit, multiple levels of interconnect networks laterallyextend with respect to the substrate surface. Interconnects formed insequential layers can be electrically connected using features such asvias or contacts. In a typical interconnect fabrication process; firstan insulating layer is formed on the semiconductor substrate, patterningand etching processes are then performed to form features or cavitiessuch as trenches, vias, and pads etc., in the insulating layer. Then,copper is electroplated to fill all the features. In such electroplatingprocesses, the wafer is placed on a wafer carrier and a cathodic (−)voltage with respect to an electrode is applied to the wafer surfacewhile a deposition electrolyte wets both the wafer surface and theelectrode.

[0005] Once the plating is over, a material removal step such as achemical mechanical polishing (CMP) process step is conducted to removethe excess copper layer, which is also called copper overburden, fromthe top surfaces (also called the field region) of the workpiece leavingcopper only in the features. An additional material removal step is thenemployed to remove the other conductive layers such as the barrier/gluelayers that are on the field region. Fabrication in this manner resultsin copper deposits within features that are physically as well aselectrically isolated from each other. Another important materialremoval technique, especially for wafers with low-k dielectrics, is theelectrochemical polishing (electropolishing) or electrochemical etchingprocess. In electropolishing, an anodic voltage is applied to the wafersurface with respect to a cathodic electrode in an electropolishingelectrolyte. Excess conductor, such as overburden copper is removedwithout physically touching and stressing the interconnect structure. Itis possible to perform electropolishing on a wafer surface whilephysically touching the surface with a pad material. Such techniques arecalled electrochemical mechanical polishing or etching methods.

[0006] Some of the adverse effects of conventional material removaltechnologies may be minimized or overcome by employing a planardeposition approach that has the ability to provide layers of planarconductive material on the workpiece surface, as well as planar removalprocesses. These planar deposition and removal processes also haveapplication in thru-resist processes employed in IC packaging. In theseapplications plating is performed into holes opened in resist layersonto seed films exposed on the bottom of each hole or opening.

[0007] One technique used for planar deposition and removal of materialsis collectively referred to as Electrochemical Mechanical Processing(ECMPR), which term is used to include Electrochemical MechanicalDeposition (ECMD) processes as well as Electrochemical Mechanicalpolishing (ECMP) which is also called Electrochemical Mechanical Etching(ECME). It should be noted that in general both ECMD and ECMP processesare referred to as electrochemical mechanical processing (ECMPR) sinceboth involve electrochemical processes and physical touching to, ormechanical action on the workpiece surface. All electrochemicaltechniques for material deposition and removal may be referred to as“electrotreatment.”

[0008] In one aspect of an ECMPR method, aworkpiece-surface-influencing-device (WSID) such as a mask, pad or asweeper is used during at least a portion of the electrotreatmentprocess when there is physical contact or close proximity and relativemotion between the workpiece surface and the WSID. Descriptions ofvarious planar deposition and planar etching methods and apparatus canbe found in the following patents and pending applications, all commonlyowned by the assignee of the present invention. U.S. Pat. No. 6,176,992entitled “Method and Apparatus for Electrochemical MechanicalDeposition.” U.S. Pat. No. 6,534,116 entitled “Plating Method andApparatus that Creates a Differential Between Additive Disposed on a TopSurface and a Cavity Surface of a Workpiece Using an ExternalInfluence,” filed on Dec. 18, 2001, and patent application Ser. No.09/961,193 filed on Sep. 20, 2001, entitled “Plating Method andApparatus for Controlling Deposition on Predetermined Portions of aWorkpiece”. These methods can deposit metals in and over cavity sectionson a workpiece in a planar manner. They also have the capability ofyielding novel structures with excess amount of metals over the featuresirrespective of their size, if desired.

[0009] In ECMD methods, the surface of the workpiece is wetted by theelectrolyte and is rendered cathodic with respect to an electrode, whichis also wetted by the electrolyte. During ECMD, the wafer surface ispushed against or in close proximity to the surface of the WSID or viceversa when relative motion between the surface of the workpiece and theWSID results in sweeping of the workpiece surface. Planar deposition isachieved due to this sweeping action as described in the above-citedpatent applications.

[0010] In ECMP methods, the surface of the workpiece is wetted by theelectropolishing electrolyte or etching solution, but the polarity ofthe applied voltage is reversed, thus rendering the workpiece surfacemore anodic compared to the electrode. A WSID touches the surface duringremoval of the layer from the workpiece surface.

[0011] Very thin planar films can be obtained by first depositing aplanar layer using an ECMD technique and then applying an ECMP techniqueon the planar film in the same electrolyte by reversing the appliedvoltage. Alternately the ECMP step can be carried out in a separatemachine and a different etching electrolyte or electropolishingsolution. This way the thickness of the deposit may be reduced in aplanar manner. In fact, an ECMP technique may be continued until all themetal on the field regions is removed. It should be noted that a WSIDmay or may not be used during the electroetching process sincesubstantially planar etching can be achieved either way as long as thestarting layer surface is planar.

[0012]FIG. 1 is a schematic illustration of an exemplary conventionalECMPR system 10 used for processing wafers. In FIG. 1, a WSID 12 havingopenings 14 in it, is disposed in close proximity of a workpiece orwafer 16 to be processed. The wafer 16 is a silicon wafer to be platedwith a conductor metal, preferably copper or copper alloy. The wafer mayor may not have a previously plated copper layer on it. The wafer 16 isretained by a wafer carrier 18 so as to position front surface 20 of thewafer against top surface 22 of the WSID 12. The openings 14 aredesigned to assure uniform deposition of copper from an electrolytesolution 24, depicted by arrows, onto the front surface 22, or uniformelectropolishing from the front surface 22. The top surface 22 of theWSID 12 facing the front surface 20 of the wafer is used as the sweeperand the WSID 12 itself establishes appropriate electrolyte flow andelectric field flow to the front surface 22 for globally uniformdeposition or electroetching. Such an ECMPR system 10 also includes anelectrode 26, which is immersed in the electrolyte 24. The electrolytesolution 24 is contained in a process chamber 25. The electrolyte 24 isin fluid communication with the electrode 26 and the front surface 20 ofthe wafer 16 through the openings 14 in the WSID 12.

[0013] It should be noted that the electrode 26 is only schematicallyshown in FIG. 1. In actual practice, the electrodes are shielded with aparticle filter and other precautions are taken to avoid bubbleaccumulation under the WSID and to avoid particles generated on theelectrode 26 to reach the surface of the wafer 16. An exemplary copperelectrolyte may be copper sulfate solution with additives such asaccelerators, suppressors, leveler, chloride and such, which arecommonly used in the industry. The top surface 22 of the WSID 12 sweepsthe front surface 20 the wafer while an electrical potential isestablished between the electrode 26 and the front surface 20 of thewafer. For deposition of a planar film such as copper, the front surfaceof the wafer 12 is made more cathodic (negative) compared to theelectrode 26, which becomes the anode. For electropolishing in the samesystem the wafer surface is made more anodic than the electrode.

[0014] U.S. application Ser. No. 09/960,236 filed on Sep. 20, 2001,entitled “Mask Plate Design,” assigned to the assignee of the presentinvention, discloses various WSID embodiments. Also, U.S. applicationSer. No. 10/155,828 filed on May 23, 2002, entitled Low ForceElectrochemical Mechanical Deposition Method and Apparatus, alsoassigned to the same assignee of the present invention teaches means ofapplying force to the wafer surface by a WSID for ECMPR.

[0015] To this end, however, while these techniques assist in obtainingplanar metal deposits or novel metal structures on workpieces andwafers, and other means of planar removal of materials from the wafersurfaces, there is still a need for further development ofhigh-throughput approaches and apparatus that can yield deposits withbetter uniformity and high yield, and methods and apparatus that providemore uniform material removal from workpiece surfaces.

SUMMARY

[0016] Present invention uniformly planarizes a conductive surface on aworkpiece during an electroplating or electropolishing process.Specifically, in electrochemical mechanical processing (ECMPR) such aselectrochemical mechanical deposition (ECMD) and electrochemicalmechanical polishing (ECMP) or electrochemical mechanical etching(ECME), since the mechanical action applied on the conductive surface onthe wafer assists planarization of the conductive surface, uniformity ofthe applied mechanical action results in uniformly planarized conductivesurfaces.

[0017] In one aspect of the present invention, a method ofelectrochemical mechanical processing of a conductive face of a wafer isprovided. The method uses a process solution, an electrode and acompressible pad having a polishing surface and a backside. Theconductive face is touched with the polishing surface of thecompressible pad and the pressure between the polishing surface and theconductive face near the center of the conductive face is increased. Theconductive face is processed while maintaining a potential differenceand a relative motion between the conductive face.

[0018] In another aspect of the present invention, a system forelectrochemical mechanical processing of a conductive face of a waferusing a process solution is provided. The system includes a compressiblepad having a polishing surface, a shaping mechanism, and an electrodefor applying a potential difference between the electrode and theconductive face as both the conductive face and the electrode are wettedby the process solution. The shaping pad is configured to push theconductive face against the polishing surface with more force at thecenter of the conductive face than the rest of the conductive face.

[0019] In another aspect of the present invention, a system forelectrochemical mechanical processing of a conductive face of a waferusing a process solution is provided. The system includes a wafercarrier holding the wafer, a solution chamber, which has an upperopening, to hold the process solution, and a compressible and flexiblepad having a polishing surface and fluid channels. The compressible andflexible pad is placed between the upper opening of the solution chamberand the conductive face of the wafer. The compressible and flexible padis configured to bow and apply more pressure near the center of theconductive face than the rest of the conductive face as the pressure ofthe process solution in the solution chamber increases.

[0020] In another aspect of the present invention, a system forelectrochemical mechanical processing of a conductive face of a waferusing a process solution is provided. The system includes a wafercarrier holding the wafer, a solution chamber to hold the processsolution, the solution chamber having an upper opening defined byextendable side walls and a compressible pad. The compressible padincludes a polishing surface and fluid openings and the compressible padis placed between the upper opening of the solution chamber and theconductive face of the wafer. As the pressure of the process solutionincreases extendable side walls of the process chamber push thepolishing surface against the conductive face and apply uniform pressureon the conductive face.

[0021] In another aspect of the present invention, a method ofelectrochemical processing of a conductive face of a wafer is provided.The method uses a process solution, an electrode and a plate, which isflexible and having channels. The process solution is flowed through thechannels and the flow of solution results in shaping the plate into aconvex shape having a top region. A central region of the conductiveface is wetted with the process solution flowing from the top region ofthe plate before wetting the rest of the conductive face. The conductiveface is processed while maintaining a potential difference between theconductive face and the electrode.

[0022] In another aspect of the present invention, a method ofelectrochemical mechanical processing of a conductive face of a wafer isprovided. The method uses a process solution, an electrode and a padwhich is flexible and compressible and having channels extending betweena polishing surface and a back surface. The polishing surface is touchedwith the conductive face and the process solution is flowed through thechannels. The flow of solution results in shaping the pad into a convexshape so that the polishing surface presses near the center of theconductive face with more force than the rest of the conductive face.Flowing the solution through the channels applies a pressure onto theback surface of the pad. The conductive face is processed whilemaintaining a potential difference between the conductive face and theelectrode.

[0023] These and other features and advantages of the present inventionwill be described below with reference to the associated drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a schematic illustration of an exemplary conventionalelectrochemical mechanical processing system;

[0025]FIG. 2 is an exemplary portion of a wafer surface with a planarconductive layer;

[0026]FIG. 3 is a schematic illustration of an electrochemicalmechanical processing system of the present invention where a force isapplied to the back surface of the wafer;

[0027]FIG. 4 is a graph showing the distribution of the applied forceover the wafer surface as the force is applied in the manner shown inFIG. 3;

[0028]FIG. 5 is a schematic illustration of interaction between a waferfront surface and the workpiece surface influencing device as the centerregion of the wafer back surface is pressed against the workpiecesurface influencing device;

[0029]FIGS. 6A-6D are schematic illustrations of various force sourcesto apply force on the back surface of a wafer;

[0030]FIG. 7 is a schematic illustration of the electrochemicalmechanical processing system of the present invention where a force isapplied to the back surface of the workpiece surface influencing device;

[0031]FIG. 8 is a schematic illustration of the interaction between awafer front surface and the workpiece surface influencing device as thesurface of the workpiece surface influencing device is pressed againstthe center region of the wafer front surface;

[0032]FIG. 9 is a graph showing the distribution of the applied forceover the wafer surface as the force is applied in the manner shown inFIG. 8;

[0033]FIG. 10 is a schematic illustration of an embodiment of a smartelectrochemical mechanical processing system of the present inventionwhere a force is applied to the back surface of the workpiece surfaceinfluencing device;

[0034]FIG. 11A-11B are schematic illustrations of various combinationsof support plate and workpiece influencing device having the convexprofile;

[0035]FIGS. 12A-14B are schematic illustrations of various thicknessplates having varying thickness and resulting degrees of bowing underthe applied pressure;

[0036]FIG. 15A-15B are schematic illustrations of removing entrappedbubbles with the present invention by bowing the WSID towards the centerof a wafer during a process; and

[0037]FIG. 16 is a schematic illustration of an alternativeelectrochemical mechanical processing system of the present inventionwhere a uniform force is applied to the front surface of the wafer by aworkpiece surface influencing device.

DETAILED DESCRIPTION

[0038] The preferred embodiments will now be described using the exampleof fabricating interconnects for integrated circuit applications. Itshould, however, be recognized that present invention can be used tooperate on any workpiece with various electroplated materials such asAu, Ag, Ni, Pt, Pd, Fe, Sn, Cr, Pb, Zn, Co and their alloys with eachother or other materials, for many different applications such aspackaging, flat panel displays, magnetic heads and such. In the examplesprovided below, the example material that is electroplated orelectropolished will be copper, but it will be understood that othermaterials can instead be used.

[0039] In electrochemical mechanical processing (ECMPR) such aselectrochemical mechanical deposition (ECMD) and electrochemicalmechanical polishing (ECMP) or etching (ECME), since the mechanicalaction on wafer surface assists planarization of the surface of thewafer, uniformity of this mechanical action is important to obtainuniform process results, such as uniformly planarized wafer surface.

[0040]FIG. 2 shows an exemplary portion of a workpiece 100 or a waferhaving a front and a back surface 101 and 102. The wafer 100 comprises asemiconductor substrate 103 and an insulation or dielectric layer 104 onwhich a planar conductive layer 106 such as a planar copper layer isformed in accordance with the process of the present invention. Thecopper layer 106 maintains a uniform overburden thickness over theentire wafer surface. The copper layer 106 is plated to fill features inthe dielectric layer using an ECMD process. Further, in an exemplaryprocess the copper layer 106 may be electropolished using ECMP. Beforethe plating process, the dielectric layer 104 is processed to formfeatures such as vias 108 and trenches 109 and 110. The features 108,109 and 110 and top surface 112 of the dielectric layer, which is oftenreferred to as field region or surface, are lined with one or moreconductive layers such as a barrier layer 114 and a copper seed layer(not shown) before forming the copper layer 106. Interconnects areformed when the copper layer 106 is removed down to the level of fieldregions 112 and the barrier layer covering the field regions is alsoremoved. Over all efficiency of this process depends on the thicknessuniformity of the copper layer 106 over the entire wafer surface. Aswill be described more fully below, the present invention provides amethod of forming a planar conductive layer while maintaining itsthickness uniformity.

[0041] During ECMD and ECMP processes, wafers are typically rotated andmay be moved laterally. As can be appreciated, on a rotating wafersurface the linear velocity due to rotation is zero right at the centerof the wafer and it increases linearly towards the edge of the wafer inproportion to the distance to the center. The linear velocity is highestright at the edge of the wafer and it is given by the relationship:V=(2πR/60) cm/second, where “r” is the radius of the wafer incentimeters and “R” is the rotation in revolution per minute (rpm). Ascan be seen from this relationship, velocity “V” increases as the radiusof the wafer “r” increases. Mechanical action delivered by a WSID (seeFIG. 1) onto wafer surface increases with the relative velocity betweenthe WSID and wafer surface as well as the force applied onto the surfaceby the WSID. Therefore, in an electrochemical mechanical process, in onemethod, the uniformity of the mechanical action on the wafer surface maybe improved by keeping the relative velocity between the WSID and thewhole wafer surface substantially the same while keeping the forceapplied by the WSID onto the wafer surface substantially constant. Anexample of this method can be found in U.S. patent application Ser. No.10/288,558, entitled Electrochemical Mechanical Deposition withAdvancible Sweeper, filed Nov. 4, 2002. In that application, a belt typeWSID is used for ECMD and ECMP processes. The belt WSID or the wafer maybe moved linearly. The high linear velocity of the belt WSID is constanteverywhere on the wafer surface as long as the velocity on the wafersurface due to rpm is much lower than the linear velocity of the beltWSID. For example, if the wafer is rotated with 5 rpm and belt linearvelocity is 100 cm/sec, the linear velocity at the edge of the wafer dueto rpm would be about 5 cm/sec for an 8″ wafer. This is negligiblecompared to the belt speed of 100 cm/sec.

[0042] In another method, if the relative velocity between the WSID andthe wafer surface is not constant, the force applied by the WSID isadjusted such that a higher force is applied onto certain surfaceregions, such as the central region of the wafer, where the relativevelocity is low. As previously mentioned, in exemplary ECMD or ECMPprocesses, the wafer is rotated and also translated over a stationaryWSID surface. If the velocity of the lateral motion is lower than themotion near the edge of the wafer due to rotation, velocity near thecenter of the wafer would be lower than at the edge. Therefore,additional force needs to be applied near the center of the wafer toimprove process results.

[0043] There are various approaches that may be used to apply additionalforce on the wafer surface near its center. One such approach involvesshaping of the wafer surface. When such shaped wafer surface is pushedagainst a pad structure, its center gets the highest force. An exampleof shaping wafer 100 while it is processed may be described inconnection with FIG. 3, which illustrates a partial view of an ECMPRsystem 200. In FIG. 3, only components such as a wafer carrier 202 and aWSID 204 of the system 200 are illustrated for the purpose of clarity.The wafer carrier holds the wafer 100 by the back surface 102 whileexposing the front surface 101 of the wafer to the WSID 204. The waferis held on a chuck face 203 of the wafer carrier.

[0044] The WSID 204 may have a compressible layer 206 having a topsurface 208. The top surface 208 may be made of a flexible material andmay be abrasive or it may contain a polishing pad material. The topsurface 208 is brought to physical contact with the front surface 101 ofthe wafer during the ECMD or ECMP processes. The WSID 204 comprisesopenings 210, such as holes with various geometrical shapes or slitswith varying width, or may be made of a porous material that allows aprocess solution (not shown) to flow through the WSID and wet thesurface of the wafer. The WSID 204 is supported by a support plate 212,which has a top surface 213 and a back surface 214. The WSID 204 isplaced on the top surface 213 of the support plate 212. The supportplate 212 is fixed on side-walls 215 of a process chamber, which is notshown in FIG. 3 but can be seen in FIG. 1. The openings 210 may continuethrough the support plate as support plate openings 216, although sizeand location of the openings 216 may be different from the openings 210in the WSID. For example, support plate openings 216 may be made ofnarrow slits or very small holes. Alternately, support plate openings216 may be larger than openings 210. Optionally a flow restrictor suchas a filter 218 may be placed under the support plate. This filter alsoreduces the number of particles that may reach the wafer surface. Aprocess solution 217 in the process chamber is delivered to the frontsurface 101 of the wafer 100. Process solution 217 flows through thepores of the filter, openings of the support plate and the WSID to reachthe front surface during the process.

[0045] Referring to FIGS. 3-5, shaping of the front surface 101 of thewafer 100 may be performed by applying a force to the back surface 102of the wafer to deflect the front surface 101. As shown in FIG. 5, asthe force is applied to the back surface of the wafer 100, the waferbows into the WSID and a higher-pressure interface 219 forms between thecenter region 220 of the front surface of the wafer and the top surface208 of the WSID 204. This is because the support plate 212 is relativelyrigid in this example and extra compression of the compressible layer ofthe WSID in the central region applies higher force to the wafer surfacein this region compared to the edge region. The size of the pressureinterface depends on the applied force and depending on the force it mayget smaller or larger. A force source in the wafer carrier 202 may applya force to the back of the wafer and cause the wafer to bow into theWSID and thereby pushing a center region 220 of the wafer 100 in thedirection of the arrow A. The force source may use a pressurized fluid,inflatable membranes, or a mechanism using shims or pins to physicallyapply force to the back surface 102 of the wafer. Application of theforce A, gives the wafer 100 and hence the front surface 101 a convexshape which allows WSID to exert more force on the center region 220than edge region 222 of the wafer 100. In FIG. 4, this can be seen inthe force distance graph 224. As seen in the graph, the force applied tothe center region is higher than the edge region of the wafer.

[0046] As shown in FIG. 5, as the force A is applied, the center regionis pushed into the WSID 204 by a distance D at the center region 220 anda distance d at the edge region 222. Since the force applied by the WSIDonto the wafer surface is proportional to the distance the surface ispressed into the WSID, as the D distance becomes larger than thed-distance, the force, which is applied to the center region becomeshigher than the edge region. It should be understood that the distancesand the convex shape of the wafer are exaggerated in figures forclarity. In practice the difference between the distance D and distanced may be in the range of 0.1-1 mm for an 8″ wafer or as much as 2 mm fora 300 mm wafer. For the purpose of clarity, openings in the WSID are notshown in FIG. 5.

[0047]FIGS. 6A-6D illustrate various configurations of force source. Ineach configuration edges of the wafer is held by a holding mechanism onthe wafer carrier and the force is applied on the back surface of thewafer. FIG. 6A shows a pressurized fluid source 230, preferably air toapply pressure to the back surface of the wafer. Fluid source may be inthe chuck face 203 of the wafer carrier (see FIG. 3). FIG. 6Billustrates an inflatable member 232 such as a bladder to fill withpressurized air or another gas to apply pressure. The bladder may beplaced between the chuck face and the back surface of the wafer, andattached to the fluid source 230. FIG. 6C shows a curved object 234,which may be placed between the back surface of the wafer and the chuckface to press against the back surface 102 of the wafer to shape it.FIG. 6D shows use of pins 236 configured to have varying length so thatmore force is applied to the center region on the back of the wafer.Pins may be placed in the chuck face and moved by a moving mechanism.

[0048] As shown in FIG. 7 in system 200, another method for achievingthe same result involves applying force to the center region of the WSID204 and thereby compressing a portion of the WSID more against thecenter region 220. As shown in FIGS. 7 and 8, since the edges of thesupport plate is substantially fixed on the side walls of the processchamber, by applying a force in the direction of arrow B to the backsurface 214 of the support plate 212, the support plate is bowed towardsthe front surface 101 of the wafer. This way, selected region 240 of thesupport plate is brought closer to the center region 220 of the wafer100 and forms a high-pressure interface 219. The location of theselected region 240 is configured to correspond to the center region 220of the wafer. The bowing effect shown in FIG. 8 and other figures arehighly exaggerated for the purpose of clarity. In practice, duringbowing, the selected region may move up a distance only in the range of0.1 to 2 millimeters. As the selected region of the support plate ismoved closer to the center region 220 of the wafer, a portion 242 of thecompressible layer 206 between the center region 220 and the selectedregion 240 is compressed between these two surfaces. This, in turn,pushes the top surface 208 of the WSID against the center region andapplies more force to the center region 220 than the edge region 222. Itshould be noted that in this method a relatively flexible support plate212 may be used. By selecting the thickness and flexibility of thesupport plate and the magnitude of the applied force, the degree ofbowing and the magnitude of the extra force applied to the centralregion may be controlled.

[0049] Referring back to FIG. 7, the force maybe applied to the supportplate 212 by exerting more process solution pressure to the back surfaceof the support plate or the filter 218 placed under it. Such pressuregives the support plate a convex shape. The pressure and thus themagnitude of the applied force may be controlled by various means suchas flow restrictors, filters with varying porosity or bleed valves.

[0050] One exemplary method of controlling force involves controllingthe flow rate of the process solution. Depending on the porosity of thefilter 218, as the flow rate of the process solution increases, thepressure under the filter 218 increases. Since the edges of the supportplate are fixed, the support plate bows up under increased processsolution flow as shown in FIG. 8. It is also possible to increase ordecrease the amount of bowing by keeping the flow constant but by usingone or more bleed valves that can control the pressure under the filter.In this case, by controlling the amount of solution that is bled throughthese valves, the pressure under the filter maybe increased (when valvesare closed restricting the amount of solution bleeding out through them)or decreased (when valves are opened increasing the amount of solutionbleeding out through them) or kept constant at a predetermined pressurelevel. It should be noted that this process may be automated usingfeedback control as will be discussed later. For the purpose of clarity,openings in the WSID are not shown in FIG. 8.

[0051] Another way of controlling the bowing and thus the force on thecentral region of the wafer involves controlling the porosity of thefilter. At a given solution flow rate, filters with smaller pore sizewould give more bowing and thus more additional force would be appliedto the central section of the wafer. As can be seen in theforce-distance graph in FIG. 9, the force applied to the center 220 ofthe wafer is higher than the force applied to the edge 222.

[0052]FIG. 10 illustrates a smart system 250 which can sense thepressure under the filter element 256 using a transducer. The system 250includes a WSID 252 supported by a support plate 254. A filter 256 isplaced under the support plate 254. The filter 256 may not be needed ifthe openings in the WSID are small enough to keep the cavity 265pressurized. However, presence of the filter is preferable since it alsofilters out any particulates from the process solution before deliveringit to the wafer surface. Process solution 258 enters chamber 260 throughan inlet 262. Differing from the previously described embodiments, apressure-monitoring device 264 such as a pressure transducer monitorsthe solution pressure and, turns on and off a bleed valve 266 to keepthe pressure, and hence the bowing of the support plate at apredetermined desired value. For example, if the flow is set to aconstant value and the pressure in the cavity 265 is higher than thepre-determined value, the bleed valve 266 is automatically opened moreto let more solution out and bring the pressure down to thepre-determined level. Similarly, if the actual pressure within cavity265 is lower than the pre-determined value then the bleed valve 266would automatically close to restrict flow through it and bring thepressure up to the pre-determined level. This way, using feedback andcomputer control a predetermined value for the pressure is selected andkept through the process. Also, by changing the pressure during theprocess, more or less force may be applied on the surface in acontrolled manner. Bowing is a strong function of the choice of filter,flexibility of the support plate and the pressure under the supportplate.

[0053] The force may also be controlled by shaping the WSID itself or byconstructing the support plate to make it more or less compliant alongthe diameter of the wafer. Other stiffeners or flexural members can beadded to WSID to produce a force curve of any desired shape forplanarization, especially at the center region.

[0054] In this respect, FIGS. 11A-11B illustrate various support plateand WSID combined structures to create a bowing effect. As shown in FIG.11A a first structure 300 includes a support plate 302 having a curvedtop surface 304. A WSID 306 is attached on the curved top surface 304 sothat a top surface 308 of the WSID is in compliance with the curved topsurface 304 of the support plate. As shown in FIG. 11B, support plateand WSID combined structure 310 has a support plate 312 and a WSID 314.In this example, a curved top surface 316 of the WSID is provided usinga curved insert 318. In FIGS. 11A-11B, for the purpose of clarityopenings of the support plates and the WSIDs are not shown in thefigures.

[0055] By varying the thickness of the support plate, applied pressureand the size of the high-pressure interface may be changed. FIGS.12A-12B illustrate a support plate 320 before and after the applicationof the force. The support plate 320 is a thin support plate; therefore,with the applied pressure it bows more in comparison to a thickersupport plate. This may allow the support plate 320 to apply morelocalized pressure and to a smaller area of the wafer.

[0056]FIGS. 13A-13B show a support plate 322, which is thicker than thesupport plate 320 described above. Since it is thicker, the supportplate bows less and thereby, it may apply a force to a larger area onthe wafer.

[0057]FIGS. 14A-14B illustrate a support plate 324 before and after theapplication of the force. The support plate 324 has a thin section 326;therefore, when a pressure is applied to the thin section, the thinsection 326 protrudes more. This may allow the support plate to applymore localized pressure and to a smaller area of the wafer. Again, thebowing effects in all these drawing are greatly exaggerated to clearlyexplain the invention. For the purpose of clarity, openings in thesupport plates are not shown in FIGS. 12A-14B.

[0058] The present invention may also be used for eliminating bubblesthat may be trapped between the wafer surface and the process solutionduring electroplating and electropolishing processes. As shown in FIG.15A, as a wafer is first lowered towards the WSID 402 and enters theprocess solution 403, bubbles 406 may get trapped under the wafersurface 404, especially near the center of the wafer. This is a commonproblem in electroplating and electropolishing technologies and isgenerally due to the fact that the edges of the wafer may get wetted bythe process solution before its center. If these bubbles stay on thewafer surface during the process, they may generate defects in theforming layers and therefore they must be removed. As shown in FIG. 15B,when the pressure of the solution 403 is increased to bow the supportplate 408 towards the wafer 400 at least during the first stage ofprocess when wafer is being lowered down towards WSID 402, WSID 402 bowsand the solution flowing from the WSID 402 also takes a convex shape.This way when the wafer is lowered towards the WSID, the central regionof the wafer gets wetted by the process solution first. Because of theconvex shape of the WSID, the solution from the top of the convex shapereaches the center of the center of the conductive surface of the waferand wets the center region before the solution flowing from the rest ofthe WSID reaches and wets the rest of the surface of the wafer. Thisway, since the bubbles are swept away from the center, no bubbleentrapment occurs. For the purpose of clarity, openings in the WSID andthe support plates are not shown in FIGS. 15A-15B.

[0059] The present invention may also be used to apply uniform forceonto the whole face of the wafer during the process. In thisapplication, a rigid support plate can be used so that the support platemoves the entire surface of the WSID towards the wafer surf ace. Onepossible embodiment is illustrated in FIG. 16. As shown in FIG. 16, anECMPR system 500 may include a WSID 502 attached on top of a supportplate 504. Edges of the support plate 504 are attached to side walls 506of the process chamber 508. In this embodiment, side walls comprisescompressible members 510. Compressible members 510 allow support plateto move vertically up and down with the applied solution pressure incavity 520. As the solution pressure in the chamber 508 within thecavity 520 is increased, rigid support plate moves towards the wafersurface and the surface of the WSID touches the entire surface of thewafer. The force applied to the surface of the wafer is uniform at eachpoint on the surface of the wafer. Those skilled in the art wouldrealize that this embodiment may be used in conjunction with all theother embodiments described so far in this application.

[0060] Although various preferred embodiments and the best mode of thepresent invention have been described in detail above, those skilled inthe art will readily appreciate that many modifications of the exemplaryembodiment are possible without materially departing from the novelteachings and advantages of this invention.

We claim:
 1. A method of electrochemical mechanical processing of aconductive face of a wafer using a process solution, an electrode and acompressible pad having a polishing surface and a backside, the methodcomprising: touching the conductive face with the polishing surface ofthe compressible pad; increasing the pressure between the polishingsurface and the conductive face near the center of the conductive face;and processing the conductive face while maintaining a potentialdifference between the conductive face and the electrode.
 2. The methodof claim 1, further comprising the step of maintaining a relative motionbetween the wafer and the compressible pad.
 3. The method of claim 2,wherein the relative motion between the wafer and the compressible padis smallest near the center of the conductive face.
 4. The method ofclaim 1, wherein the step of increasing the pressure near the center ofthe conductive face comprises shaping the wafer so that the center ofthe conductive face is pressed against the polishing surface with moreforce than the rest of the conductive face.
 5. The method of claim 1,wherein the step of increasing the pressure near the center of theconductive face comprises shaping the pad so that the polishing surfaceapplies more pressure to the center of the conductive face than to therest of the conductive face.
 6. The method of claim 4, wherein theshaping the wafer is provided by applying a force to the center of aback face of the wafer.
 7. The method of claim 6, wherein the force isapplied by an inflatable membrane.
 8. The method of claim 6, wherein theforce is applied by pushing at least one pin.
 9. The method of claim 6,wherein the force is applied by placing a curved surface onto the backface of the wafer.
 10. The method of claim 5, wherein shaping the pad isprovided by applying a force onto the backside of the compressible pad.11. The method of claim 10, wherein the force is applied by exertingliquid pressure onto the backside of the compressible pad.
 12. Themethod of claim 10, wherein the force is applied as the process solutionflows through the compressible pad.
 13. The method of claim 12, furthercomprising controlling the force by controlling the liquid pressure. 14.The method of claim 12, further comprising the step of controlling theflow rate of the process solution to adjust the force applied to thebackside of the compressible pad.
 15. The method of claim 1, wherein thestep of processing comprises electrochemical mechanical deposition. 16.The method of claim 1, wherein the step of processing compriseselectrochemical mechanical polishing.
 17. A system for electrochemicalmechanical processing of a conductive face of a wafer using a processsolution, comprising: a compressible pad having a polishing surface; ashaping mechanism configured to push the conductive face against thepolishing surface with more force at the center of the conductive facethan the rest of the conductive face; and an electrode for applying apotential difference between the electrode and the conductive face asboth the conductive face and the electrode are wetted by the processsolution.
 18. The system of claim 17, further comprising a movingmechanism configured to provide relative motion between the conductiveface and the polishing surface during the process.
 19. The system ofclaim 17, wherein the shaping mechanism applies pressure on a back faceof the wafer to push the center of the conductive face against thepolishing surface with more force than the rest of the conductive face.20. The system of claim 19, wherein the shaping mechanism is a convexsurface that is pressed on the back face of the wafer.
 21. The system ofclaim 19, wherein the shaping mechanism is at least one movable pin thatis placed on the back face of the wafer.
 22. The system of claim 19,wherein the shaping mechanism is an inflatable membrane exertingpressure on the back face of the wafer.
 23. The system of claim 17,further comprising a wafer holder to retain the wafer.
 24. The system ofclaim 23, wherein the pressure mechanism is a part of the wafer holder.25. The system of claim 24, wherein the shaping mechanism appliespressure on a back face of the wafer to push the center of theconductive face against the polishing surface with more force than therest of the conductive face.
 26. The system of claim 25, wherein thepressure mechanism is a convex surface that is pressed on the back faceof the wafer.
 27. The system of claim 25, wherein the pressure mechanismis at least one movable pin that is placed on the back face of thewafer.
 28. The system of claim 25, wherein the pressure mechanism is aninflatable membrane exerting pressure on the back face of the wafer. 29.The system of claim 17, wherein electrochemical mechanical processingcomprises electrochemical mechanical deposition.
 30. The system of claim17, wherein electrochemical mechanical processing compriseselectrochemical mechanical polishing.
 31. A system for electrochemicalmechanical processing of a conductive face of a wafer using a processsolution, comprising: a wafer carrier holding the wafer; a solutionchamber to hold the process solution, the solution chamber having anupper opening; and a compressible and flexible pad, having a polishingsurface and fluid channels, placed between the upper opening of thesolution chamber and the conductive face of the wafer, wherein thecompressible and flexible pad is configured to bow and apply morepressure near the center of the conductive face than the rest of theconductive face as the pressure of the process solution in the solutionchamber increases.
 32. The system of claim 31, further comprising aperforated and flexible support plate placed under the compressible andflexible pad.
 33. The system of claim 31, further comprising a porousmembrane placed under the compressible and flexible pad.
 34. The systemof claim 32, wherein a porous membrane is placed under the perforatedand flexible support plate.
 35. The system of claim 31 furthercomprising a pressure sensor placed in fluid communication with theprocess in the process solution chamber.
 36. The system of claim 31,wherein the signal of the pressure sensor is fed to a solution flowcontroller to adjust flow rate of the process solution.
 37. The systemof claim 31, wherein electrochemical mechanical processing compriseselectrochemical mechanical deposition.
 38. The system of claim 31,wherein electrochemical mechanical processing comprises electrochemicalmechanical polishing.
 39. A system for electrochemical mechanicalprocessing of a conductive face of a wafer using a process solution,comprising: a wafer carrier holding the wafer; a solution chamber tohold the process solution, the solution chamber having an upper openingdefined by extendable side walls; and a compressible pad, having apolishing surface and fluid openings, placed between the upper openingof the solution chamber and the conductive face of the wafer, wherein asthe pressure of the process solution increases extendable side walls ofthe process chamber push the polishing surface against the conductiveface and apply uniform pressure on the conductive face.
 40. The systemof claim 39, further comprising a perforated support plate placed underthe compressible pad.
 41. The system of claim 39, further comprising aporous membrane placed under the compressible pad.
 42. The system ofclaim 41, wherein a porous membrane is placed under the perforatedsupport plate.
 43. The system of claim 39, wherein electrochemicalmechanical processing comprises electrochemical mechanical deposition.44. The system of claim 39, wherein electrochemical mechanicalprocessing comprises electrochemical mechanical polishing.
 45. A methodof electrochemical processing of a conductive face of a wafer using aprocess solution, an electrode and a plate, which is flexible, havingchannels, the method comprising: flowing the process solution throughthe channels wherein the flow of solution results in shaping the plateinto a convex shape having a top region; wetting a central region of theconductive face with the process solution flowing from the top region ofthe plate before wetting the rest of the conductive face; and processingthe conductive face while maintaining a potential difference between theconductive face and the electrode.
 46. The method of claim 45 furthercomprising the step of moving the conductive face towards the platebefore the step of wetting.
 47. The method of claim 46, wherein the stepof wetting the central region of the conductive face results in removingentrapped gas bubbles from the central region.
 48. The method of claim45, further comprising rotating the wafer.
 49. The method of claim 45,wherein the step of processing comprises electrochemical deposition. 50.The method of claim 45, wherein the step of processing compriseselectrochemical polishing.
 51. The method of claim 45, wherein a pad isattached onto the plate.
 52. The method of claim 51, wherein the step ofprocessing comprises electrochemical mechanical processing.
 53. A methodof electrochemical mechanical processing of a conductive face of a waferusing a process solution, an electrode and a pad which is flexible andcompressible and having channels extending between a polishing surfaceand a back surface, the method comprising: touching the polishingsurface with the conductive face flowing the process solution throughthe channels wherein the flow of solution results in shaping the padinto a convex shape so that the polishing surface presses near thecenter of the conductive face with more force than the rest of theconductive face; and processing the conductive face while maintaining apotential difference between the conductive face and the electrode. 54.The method of claim 53, wherein flowing of the solution through thechannels applies a pressure onto the back surface of the pad.
 55. Themethod of claim 54, wherein the pressure is controlled by the flow rateof the process solution.
 56. The method of claim 53, further comprisingthe step of maintaining a relative motion between the wafer and thecompressible pad.
 57. The method of claim 53, wherein the step ofprocessing comprises electrochemical mechanical deposition.
 58. Themethod of claim 53, wherein the step of processing compriseselectrochemical mechanical polishing.